Values to straighten wave texture?
It is probably just easier to recreate it using math nodes rather than trying to align it to axis.

Use a Math Node set to Cosine; as input use your desired texture coordinates like Object or Generated.

Add a Separate XYZ node and use the desired axis as direction, then multiply it by any value to control density of the waves.



You can still run the output through a color ramp node to control progression and color, and covert the whole thing into a node group for simplicity sake, to make it visually cleaner, easier to reuse or port to other files.